1. Field of the Invention
The present invention pertains to a composition of superactive fluorocarbonated products useful as bases or starting materials for the manufacture of fire extinguishing mixtures and having particular utility in combating hydrocarbon fires.
2. Description of the Prior Art
The efficacy of the compositions of the present invention as fire extinguishing agents depends essentially on their film-forming properties and on the solidity or strength of the films produced. It is moreover additionally advantageous that these solutions have good foaming properties, since the most commonly employed method of combating fire comprises projecting the solution at the base of the fire in the form of a foam. Unfortunately, the foam itself does not resist the heat radiated from adjacent localities or parts of the fire as well as would be desired, and the action of the foam should be supplemented by the formation of a film which is impermeable to the vapors [products of combustion] and resulting from spreading of the solution. The film actually consists of a colloidal fluorinated membrane which adheres to the surface of the hydrocarbon and which supports a liquid film of the aqueous surface-active solution, according to the principle which is well known under the name of "light water" and which is described in U.S. Pat. No. 3,258,423.
The film has several functions, first it isolates the combustible material from the oxygen of the atmosphere, further since it releases water vapor directly at the base of the flames it thereby retards combustion, and finally it functions as a thermal screen, that is as an insulator, between the combustible material and the vapors that are already in the process of burning.
It is known that a liquid, B, can spread on a liquid, A, only if the work of adhesion, T.sub.AB, corresponding to the formation of the interface AB, is greater than the work of cohesion of the liquid B, T.sub.cohB, which work of cohesion is equal to twice the surface tension, X.sub.B. If T.sub.AB is replaced by the value for it in the Dupre equation and if the spreading coefficient, S, denotes the quantity T.sub.AB - T.sub.cohB, then the condition for spreading can be written as EQU S = (.gamma..sub.A +.gamma..sub.B - .gamma..sub.AB) - 2.gamma..sub.B &gt;0,
wherein
.gamma..sub.AB is the interfacial tension between the liquids A and B, i.e. EQU S = .gamma..sub.A - (.gamma..sub.B +.gamma. .sub.AB) &gt; 0
these quantities are directly determinable from experimentation and conequently it is possible to predict the behavior of the two immiscible liquids in presence of each other.
The above formulae show that the spreading properties of the aqueous surface-active solutions will be inversely related to their surface tension and to their interfacial tension with respect to the hydrocarbon. The interfacial tension is determined by the molecular structure of the compounds and the polar interactions which can result therefrom, and has only a small effect on aliphatic hydrocarbons.
The surface tension of an aqueous solution can be reduced by increasing the concentration of the surface-active agent, however, there is a limit to achieving a reduction in this manner, due to the critical micellar concentration beyond which it is not possible to obtain a decreased value.
In practice, the majority of the fluorinated surface-active compounds which are described in the literature, and particularly those cited in French patents Nos. 1,405,794 and 2,035,584, and in U.S. Pat. Nos. 2,764,602 and 3,258,423, do not permit the formation of durable films on hydrocarbons whose surface tension is lower than 22 to 23 dynes per centimeter, for example, high octane gasoline whose surface tension is 22.4 dynes/cm.